Study of graphene growth on a metal and of nanoparticles on top

High quality preparation, by chemical vapor deposition on metals, has opened a route to future applications exploiting the exceptional properties of graphene a ppearing in high quality samples. Metallic substrates are also rich playgrounds allowing for probing some of the unique properties of graphene, to manipulate them, and to build up advanced nanosystems based on graphene. During my PhD works performed within the framework of a collaboration between CEA-INAC and Institut Néel, I have been addressing a specific system, graphene on Ir(111), which is a prototype of quasi-free-standing graphene, characterized by a weak graphene-metal interaction and a very high quality. I have studied the structure of bare graphene on Ir(111) and of few ten-atoms-metallic nanoparticles, organized with great degree of order onto graphene/Ir(111), by means of diffraction techniques. In particular, I have used surface X-ray diffraction, as available at the European Synchrotron Radiation Facility whose high brilliance makes it possible to probe such a low amount of weakly scattering matter as contained in single-layer graphene. Our experiments were performed in situ, inside a ultra-high vacuum chamber where the samples were prepared, and as a function of temperature. During my defense I will discuss (i) the positive thermal expansion coefficient of graphene onto Ir(111), which is at variance to the expectation for a quasi-free-standing graphene, (ii) the fine structure of the graphene and Ir(111) nanorippling along a superstructure (a moiré) they form due their lattice mismatch, and (iii) the small size effects which govern the structure of nanoparticles organized onto the moiré as well as the structural modifications their growth induces into graphene.